The aqueous polymer compositions are stable at high temperatures against thermal, chemical and mechanical degradation. The new compositions are useful for tertiary recovery processes, in drilling muds and cementing additives, as completion fluid viscosifiers, as friction reducers, for water control purposes, for hydraulic fracturing and acidizing processes, for lubrication additives, corrosion inhibitors, metal working fluids, mining, and protective colloids.
There have been several attempts of aqueous polymer compositions stabilized against degradation.
United States Patent Application Publication No. 2006/0027364 discloses an aqueous, viscoelastic treating fluid gelled with a crosslinked guar or guar derivative. The viscosity of this treating fluid and the thermal stabilization is improved by addition of a glycol.
U.S. Pat. No. 5,103,913 discloses aqueous fracturing fluids with improved temperature stability. These fluids contain guar gelling agent and a soluble bicarbonate. As shown in the patent examples these fluids are applicable for operations in the temperature range between 175° C. and 210° C.
U.S. Pat. No. 4,801,389 discloses aqueous fracturing fluids with improved temperature stability. These fluids contain guar gelling agent, zirconium or hafnium crosslinking agent and a bicarbonate salt. These fluids are applicable for operations in the temperature range between 80 and 120° C.
U.S. Pat. No. 4,721,577 discloses stabilized fracturing fluids with improved temperature stability. These fluids contain guar gelling agent and thiol derivatives of selected heterocyclic compounds. These fluids are applicable for operations in the temperature range between 90 and 200° C.
U.S. Pat. No. 4,686,052 discloses gels derived from solvatable polysaccharides and crosslinked with titanium or zirconium compounds. These gels are stabilized against shear degradation at elevated temperature by addition of an alkanolamine.
Canadian Publication No. 2,467,791 discloses dry blended particulate compositions for well treating comprising a particulate hydratable polysaccharide, a particulate crosslinking agent, a particulate base and a particulate sodium, potassium or ammonium pyrophosphate or oxalate. As a thermal stabilizer sodium thiosulfate is proposed.
WIPO Publication No. WO 97/04038 discloses a drilling fluid comprising a selected base fluid and at least one additive. The base fluid is a synthetic fluid. Heat stabilization or addition of heat stabilizers is not disclosed.
U.S. Pat. No. 4,661,266 discloses a completion fluid comprising a polymer, hydroxyethyl cellulose, and a stabilizer. The stabilizer is benzothiazole or a thiadiazole derivative. Said composition exhibits a superior stability of the rheological properties under elevated temperatures. The tested temperature is 110 to 130° C.
U.S. Pat. No. 4,795,575 discloses a stabilized polymer thickened aqueous composition used in an oil recovery process, based on the use of mercaptobenzothiazole as stabilizer. The polymers used are partially hydrolyzed polyacrylamide polymers or copolymers. The pH of the aqueous composition is between 10 and 13. The applied temperature is between 50 and 80° C.
In the last years, commercially successful exploration of subterranean deposits has become more difficult because the subterranean deposits are prospected in a deeper stratum. For this reason, the temperature of the stratum tends to rise and, in many cases, it reaches 150° C. or more. At such high temperatures, the applied polymers deteriorate, for example by thermal, chemical or physical stress degradation. This leads to a reduction in rheological properties of the aqueous polymer composition and creates a serious obstacle in high temperature applications. Accordingly, the inherent functions of the aqueous polymer composition fluid can be satisfactorily obtained only if degradation (e.g., caused by decomposition) of its rheological and chemical properties can be prevented even at elevated temperatures.
It would be desirable if a composition and method could be devised to stabilize and enhance the performance of aqueous polymer compositions such as used in drilling muds and for tertiary recovery.
The present invention is intended to overcome the above problems and an object of the present invention is to provide stabilized aqueous polymer compositions.